I wrote a kinda lengthy blog post about doing this sort of thing:
http://freedomandbeer.com/posts/extensible-xml-with-xml-namespaces-and-relaxng
RelaxNG is a fantastic language for specifying schemas for XML - the
grammar notation is very natural to write in. Allowed elements are
specified using "name classes", and you can perform set arithmetic
over those classes to achieve some amazing results for extensibility,
by delegating validation of extension elements to the author of the
extensions, while retaining the ability to assert the validity of the
core document structure.
If I understand the problem that you're trying to solve here, it is
exactly analogous to the example in my blog post. I think you would
probably structure your xml somewhat differently than below - you
define the "profile" namespace prefix on the <extension> element, but
since the profile isn't a child of that element, the declaration
doesn't carry through. For your goals here, I don't even think the
<extension> element buys you anything -- what you really want to do,
it seems, is change the core Maven schema to allow arbitrary
extensions to a project's XML, as long as they are partitioned into a
new namespace - rewriting your example XML:
<project xmlns="http://maven.apache.org/POM/4.0.0";>
...
<profile xmlns:profile="http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
">
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<profile:deactivation>
<profile:os>
<profile:name>Windows 98</profile:name>
<profile:os>
</profile:deactivation>
</profile>
...
</project>
Using RelaxNG, you could write the rule for the <profile> element to
allow any element NOT in the maven namespace to be included:
PROFILE =
element maven:profile {
element maven:activation {
element maven:activeByDefault { xsd:boolean}
}
| ANY_EXT_ELEMENT*
}
ANY_EXT_ELEMENT =
element * - maven:* {
attribute * { text }*,
( text* & ANY_EXT_ELEMENT* )*
}
And then, you could declare a RelaxNG grammar to parse a "project with
profile enancements" document like:
include "maven.rnc" {
ANY_EXT_ELEMENT =
element * - (maven:* | profile:*) {
attribute * { text }*,
( text* & ANY_EXT_ELEMENT* )*
}
| DEACTIVATION
}
DEACTIVATION =
element profile:deactivation {
element profile:os {
element profile:name { text }
}
}
Like I said, there's a much more detailed, and analogous, example at
the link above. hope this helps!
- Bryon
On May 16, 2008, at 1:53 PM, nicolas de loof wrote:
Hello,
many thread on this list makes proposal for some changes in the
POM.xml
format, to be included in 4.1.0 modelVersion.
Could we use XML namespaces to support progressive enhancements ?
Based on
this, proposal for new features could be added to maven, using an
<extension> to support the new schema, without requirement to wait
for next
major version to include POM structure changes.
example : considering the recent proposal for profiles enhancements
http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
<profile>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<deactivation>
<os>
<name>Windows 98</name>
</os>
</deactivation>
</profile>
Could be rewritten :
<extensions>
<extension xmlns:profile=
http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
<groupId>org.apache.maven.proposals</groupId>
<artifactId>profile-enhancements</artifactId>
</extension>
<extensions>
<profile>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<profile:deactivation>
<profile:os>
<profile:name>Windows 98</profile:name>
</profile:os>
</profile:deactivation>
</profile>
This can be compared with namespace support in Springframework
context files
: adding a new custom namespace allow to make the configuration less
verbose
or more powerfull, with no requirement to change the base XML model.
Nicolas
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